The Chicago Architecture Center's Open House Chicago (OHC) is the city's annual architecture festival. For one weekend in October you can explore Chicago's most iconic and unique architectural treasures. From mansions to sacred spaces, theaters to private clubs, hotels to secret rooms - OHC gives visitors a behind-the-scenes look at over 250 of Chicago's great spaces that are rarely, if ever, open to the public. October 19 and 20; 10 am - 5 pm. This event takes place throughout the city and in Evanston and Oak Park.